首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   27823篇
  免费   708篇
  国内免费   5篇
财政金融   4036篇
工业经济   1609篇
计划管理   3924篇
经济学   5385篇
综合类   244篇
运输经济   176篇
旅游经济   341篇
贸易经济   3779篇
农业经济   1140篇
经济概况   2606篇
水利工程   5219篇
信息产业经济   3篇
邮电经济   74篇
  2021年   222篇
  2020年   337篇
  2019年   539篇
  2018年   655篇
  2017年   659篇
  2016年   678篇
  2015年   446篇
  2014年   685篇
  2013年   2636篇
  2012年   1101篇
  2011年   1057篇
  2010年   802篇
  2009年   875篇
  2008年   937篇
  2007年   958篇
  2006年   954篇
  2005年   819篇
  2004年   760篇
  2003年   539篇
  2002年   486篇
  2001年   577篇
  2000年   494篇
  1999年   470篇
  1998年   512篇
  1997年   476篇
  1996年   471篇
  1995年   414篇
  1994年   406篇
  1993年   398篇
  1992年   411篇
  1991年   425篇
  1990年   384篇
  1989年   304篇
  1988年   319篇
  1987年   316篇
  1986年   285篇
  1985年   402篇
  1984年   394篇
  1983年   371篇
  1982年   330篇
  1981年   330篇
  1980年   352篇
  1979年   333篇
  1978年   285篇
  1977年   232篇
  1976年   249篇
  1975年   206篇
  1974年   202篇
  1973年   203篇
  1972年   152篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
The historic focus of new products research has been on the ability of new products to enhance the profitability and competitive position of the innovating firm. In this article, Timothy Devinney shows that there exists an overlooked and potentially significant side effect associated with new product innovations: financial risk changes. He reports that significant financial risk changes occurred in approximately 50% of the new product announcements he examined. The magnitude of these financial risk changes translates into overestimates or underestimates of the firm's cost of capital by 17% to 18% and is strongly and positively related to the size of the firm and the firm's new product innovation activity.  相似文献   
73.
74.
Summary A sequential testing procedure called 2-SPRT for the meanμ of the negative binomial distribution with known exponentk is presented. For any fixedμ 0(μ 1<μ 0<μ 2), the 2-SPRT provides an asymptotic solution to the modified Kiefer-Weiss problem. Determination ofμ 0 such that the test provides an approximate solution to the Kiefer-Weiss problem is described. The behavior of the 2-SPRT and the Sequential Probability Ratio Test is investigated using Monte Carlo methods. The error probabilities and the average sample numbers are compared. All the computations were carried out on the Alabama Supercomputer.  相似文献   
75.
A two-dimensional cross-section finite difference model is presented to simulate density dependent leachate migration in leaky aquifers. Unlike existing models, a new approach is adopted to couple the groundwater-flow equation and the hydrodynamic dispersion equation with the elimination of the intermediate step of calculating velocities. The concept of the reference density is employed, permitting increased accuracy (over pressure-based models) in the representation of the transport process. The model is then used to study the effect of several hydraulic and transport parameters on the flow pattern and plume migration which are found to be very sensitive to most of these parameters. Equiconcentration and equipotential lines are overlapped to provide a better understanding of the coupling effect.  相似文献   
76.
Dr. M. Riedel 《Metrika》1992,39(1):209-217
Summary In this note we characterize all linear transformations of random vectors which are invariant for a given parametric covariance family. Two one-dimensional covariance families are discussed in detail.  相似文献   
77.
Summary In The Netherlands public debt management is in the hands of the budgetary policy-maker, whose recourse to the capital market can exceed or fall short of the total borrowing requirement in order to absorb or create liquidity. The conduct of that policy since the early 1960's is analyzed in this paper, emphasizing the importance of medium-term control over the public finances as a prerequisite for the ability of debt management to make a flexible contribution to monetary policy. During the 1960's this condition was satisfied and debt management followed a stable countercyclical pattern which, however, was abandoned after the early 1970's as the public finances swung into substantial disequilibrium.The author thanks J. Boughton, L. Bovenberg, D. Hendry, P. Masson, J. Muellbauer, and the referees for comments on earlier versions. However, the views expressed are his alone and do not necessarily represent those of the International Monetary Fund.  相似文献   
78.
Fertilisers may contain pollutants that are applied to the field together with the nutrients. Comparing fertilisers is difficult because of their different concentrations of nutrients and pollutants. In this study an already existing model was taken. It was further developed to compare nutrient fluxes (N, P, K, Ca, Mg, S, humus) and pollutants (heavy metals and pharmaceuticals) of pig and cattle slurry as well as human urine. The data used is taken from literature and, in the case of pharmaceuticals in urine, daily excretion rates were calculated. An amount of 19 m3 ha(-1) a(-1) undiluted urine can be applied, limiting factor is sulphur. Without taking over-fertilisation into account, an addition of mineral fertiliser is required to any organic fertiliser application. In general, heavy metal, antibiotic, and hormone fluxes are higher by using animal manure then urine as fertiliser. However, additional loads of other pharmaceuticals consumed by humans have to be considered. Overall, the model is a suitable tool worthwhile to be extended in aspects of hygiene, environmental impacts as for example, degradation processes as well as ecotoxicology.  相似文献   
79.
The San Diego County Water Authority of California has initiated planning for coastal desalination facilities to augment their water supplies. Integration of the different water qualities from these facilities into existing pipelines must be achieved. This investigation determined whether, and to what degree, consumers can discriminate between desalinated seawater and imported water supplies and how these investigations can contribute to decision making regarding the need for construction of facilities to blend such supplies prior to delivery. Based upon the results of the flavour profile analysis panel and the consumer evaluation sessions, it was concluded that free chlorine versus chloramine disinfection or different concentrations of disinfectants did not significantly affect consumer perception of the taste and odour of desalinated seawater or blends with Colorado River water and State project water. Consumers were able to discern between desalinated seawater and imported water, preferring imported water when forced to make a choice. However, the investigators did not believe that the difference in consumer perception was significant enough to warrant special blending facilities to mitigate the relatively minor aesthetic quality differences between imported water supplies and desalinated seawater.  相似文献   
80.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号